docs: Document the DDEV install

Problem/Motivation

The README only covered a bare Composer install, with nothing for DDEV.

Steps to reproduce

Follow the README to install Cucumber Project Template via DDEV; no DDEV steps existed.

Proposed resolution

Document the full DDEV flow end to end: ddev config, ddev start, ddev composer create-project drupal/cucumber_project:~12.0, ddev restart, ddev drush site:install cucumber, ddev launch, plus a short note for installing without DDEV. Note that the template's own .ddev/config.yaml lands during ddev composer create-project and overwrites the one ddev config wrote, so a ddev restart is needed; and that ddev drush finds bin/drush despite the non-standard bin-dir. Verified end to end on Drupal 11.4 with PHP 8.4: installation completes.

Remaining tasks

• ✅ File an issue about this project
• ❌ Addition/Change/Update/Fix to this project
• ❌ Testing to ensure no regression
• ➕ Automated unit/functional testing coverage
• ➕ Developer Documentation support on feature change/addition
• ➕ User Guide Documentation support on feature change/addition
• ➕ UX/UI designer responsibilities
• ➕ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ❌ Credit contributors
• ❌ Review with the product owner
• ❌ Update Release Notes
• ❌ Release

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• N/A